Bowdens
Contact Timer (HV Circuit Breaker Opening / Closing Timer)

Bowdens Contact Timer Circuit Breaker

• HV Circuit Breaker Opening and Closing Timer

Bowdens Contact Timer measures the exact circuit breaker opening or closing time. Timing starts from the moment that the DC trip or closing contacts ‘make, to the instant there is either a loss of current in the protection CT secondary for an opening time, or the appearance of current in the protection CT secondary for a closing time.

The Contact Timer is presented in a tough ABS pocket sized case. It is powered by a PP3 Alkaline battery and provides a clear LCD read-out of time in milliseconds.

Crocodile clip leads are provided with the instrument to make the necessary connections to the DC circuit and a clip-on CT is provided for the AC connection.

The instrument can be switched on/off by the slide switch on the side of the case. As a precaution against unnecessary battery drain the timer incorporates an auto-switch off facility, which functions 30 minutes after the last reading.

The front display has a yellow switch for the change-over from opening to closing times and a soft touch reset switch to allow the previous time read-out to be reset to zero.

Circuit Breaker Timer Key Features:

• Measures the exact opening and closing time of circuit time of circuit breaker main contacts
• Use on circuit breakers in service position
• Identifies the slow operating mechanism
• Takes seconds to connect
• Clear read-out display in milliseconds
• Pocket sized instrument

6 Reasons Why a HV Circuit Breaker Opening & Closing Timer is Important

An HV Circuit Breaker Opening and Closing Timer is a vital diagnostic and maintenance tool in electrical power systems. It measures the precise time an HV Circuit Breaker takes to open (interrupt fault current) and close (restore normal operation) after receiving a command. Accurate timing is crucial because even small delays can affect protection, stability, and safety of the power grid.

1. Ensures System Reliability

• The HV Circuit Breaker is the first protective barrier against short circuits and overloads.
• If it opens too slowly, fault current may remain in the system, risking transformer or generator damage.
• If it closes incorrectly, it can cause power instability or failure to restore supply on time.

2. Condition Monitoring & Predictive Maintenance

• Over time, an HV Circuit Breaker is subject to spring wear, contact erosion, or lubrication problems.
• Delayed opening and closing times highlight early warning signs of mechanical or electrical deterioration.
• Routine monitoring with a timer helps plan predictive maintenance before unexpected failures occur.

3. Compliance with Standards

• International standards like IEC and IEEE define acceptable operating times for HV Circuit Breakers.
• Timing tests confirm that the breaker continues to perform within those limits throughout its life cycle.
• Failure to comply may compromise grid reliability and violate regulatory requirements.

4. Protection Relay Coordination

• Protection relays are calibrated based on the expected response of the HV Circuit Breaker.
• If the breaker response deviates, relay coordination is affected, leading to mis-tripping or extended outages.
• Regular timer testing ensures the protection scheme operates as designed.

5. Safety for Personnel and Equipment

• A delayed HV Circuit Breaker opening may cause dangerous arc flash events or excessive fault current exposure.
• Accurate timing ensures the breaker operates quickly and safely, minimizing risks to staff and equipment.

6. Verification after Repairs or Commissioning

• After installation, major repair, or refurbishment, timing tests verify that the HV Circuit Breaker is fit for service.
• It confirms that upgrades or adjustments have not affected its mechanical and electrical performance.

The Takeaway

The HV Circuit Breaker Opening and Closing Timer is essential to confirm that breakers work within safe, reliable, and standard-compliant limits. By ensuring correct operation, it protects equipment, safeguards personnel, and preserves system stability. Without such testing, hidden issues in an HV Circuit Breaker may only be revealed during an actual fault - when consequences can be catastrophic.